This invention relates to an LED backlight device and an LCD device using the LED backlight device.
In a general LCD (Liquid Crystal Display) device, a light is emitted by a light source, and is incident on an LCD panel. The LCD device is configured to change molecular alignments of liquid crystals (pixels) arranged on the LCD panel, so as to display an image using the light passing through the LCD panel.
The light source used in such an LCD device is called as a backlight, since the light source is disposed on the backside of the LCD panel (i.e., the side opposite to a display surface of the LCD panel). The conventional light source is composed of a cold cathode ray tube or a semiconductor light emitting element. The light source using the semiconductor light emitting element has been broadly used, since such a light source has a long lifetime and contributes to reduction of power consumption.
In this regard, there is known a surface-emitting light source that uses an LED (Light Emitting Diode) as the above described semiconductor light emitting element. Such a surface-emitting light source has a plate-like member called as a light guiding plate or a light diffusion plate for guiding the light emitted by the LED. The light emitted by the LED is incident on an end surface of the light guiding plate. The light guiding plate reflects and diffuses the incident light in the direction perpendicular to the surface of the light guiding plate, and emits the light from a surface thereof (see Patent Document No. 1).
Patent Document No. 1: Japanese Laid-Open Patent Publication No. 11-232920.
However, in the conventional backlight device, the light diffused in the interior of the light guiding plate tends to attenuate due to the reflection and diffusion, as a distance from the incident surface (i.e., the end surface of the light guiding plate) increases. Therefore, in order to obtain a high light intensity uniformly over the entire surface, the structure of the light guiding plate needs to be complicated, and the LED backlight device needs to be thick.